"THE DOCTOR IS IN"
(7/13/08)
Excerpted from:
The ARRL Letter
Vol. 27, No. 27
July 11, 2008
This week, ARRL Letter readers are in luck! The ARRL's very own Doctor, author of the popular QST column "The Doctor Is IN," answers a question from his mailbag:
Question -- Don Christensen, W8WOJ, of Midland, Michigan, asks: I am not a frequent user of 2 meters yet; however, I do want to be available for emergency activity. I have a 2 meter handheld transceiver at the ready, but wonder what the preferred procedure is to ensure that my transceiver's nickel-cadmium (NiCd) batteries are charged and ready for service.
The Doctor answers -- Unfortunately, NiCds might not be the best choice for such an application with intermittent use.
If you run down a NiCd battery pack too low, any strong cells may reverse charge the weaker cells, damaging the weak cells. On the other hand they also don't like being constantly topped off without actual hard use -- this promotes crystal formation, which can short out the cells. They are most happy in applications in which they are used until they discharge significantly, but not all the way and then are just charged until fully recharged. Thus, the idea of having a spare pack that is just kept charged up, but never actually used, is not a good plan.
If you have two packs, they will both last longer if one is used until it runs down and then you switch to the other and promptly recharge the depleted one. Perhaps you can have the radio turned on a few days a week monitoring the local repeater.
Many handheld radios offer battery cases for non-rechargeable Alkaline cells that can be used in place of the rechargeable battery. These are a good choice since they have long shelf life, generally have a longer operating life than a charge with similar sized NiCds, and are usable in field situations in which charging sources are not available.
Another choice, if you must have a rechargeable battery, is to use sealed lead acid or gel cell batteries -- they love to be kept on a float charge until needed, but are bulky and require a separate cable to the handheld.